A liquid crystal display device comprises a liquid crystal cell and polarizing plate(s). A polarizing plate comprises protective film(s) generally composed of cellulose acetate, and a polarizing film, and is obtained typically by dying the polarizing film composed of polyvinyl alcohol film with iodine, stretching, and being stacked on both surfaces thereof with protective film(s). A transmission-type liquid crystal display device generally comprises two polarizing plates disposed both sides of the liquid crystal cell, and further comprises one or more optical compensation films; whereas a reflection-type liquid crystal display device generally comprises a reflection plate, a liquid crystal cell, one or more optical compensation film(s), and a polarizing plate in this order. A liquid crystal cell is composed of liquid crystalline molecules, two substrates enclosing them in between, and electrode layers applying therethrough voltage to the liquid crystalline molecules. The liquid crystal cell provides ON/OFF states based on difference in aligned states of the liquid crystalline molecules; and various displaying modes applicable to both of transmission and reflection types such as TN (twisted nematic), IPS (in-plane switching), OCB (optically compensatory bend), VA (vertically aligned), and ECB (electrically controlled birefringence) modes have been proposed.
In recent years, an OCB mode (or bend mode), characterized by its rapid response, has been attracting more attention under increasing needs of liquid crystal television sets. In the OCB mode, retardation of the liquid crystal cell is compensated by the optical compensation film(s) in principle, and therefore matching of optical characteristics between the optical compensation films and the liquid crystal cell are required for achieving wide viewing angle characteristics, viewing angle dependence capable of ensuring desirable hue, and strong blackness in the black state. For example, Japanese Laid-Open Patent Publication Nos. H9-211444 and H11-316378 disclose OCB-mode liquid crystal display devices provided with optical compensation films formed of liquid crystalline compounds. It has, however, been difficult to obtain desirable viewing angle characteristics, simply by controlling ever-known parameters as described in these publications. Japanese Laid-Open Patent Publication Nos. H8-101381 and H9-329785 disclose improvement in wavelength-dependence of the optical compensation film. These publications disclose techniques of improving optical characteristics of materials used for producing the optical compensation films and the liquid crystal cell, however, further improvement for better black state and for viewing angle dependence in contrast and hue has still required. For overcoming these problems, Japanese Laid-Open Patent Publication No. H9-230332 discloses the multi-gap technique in which transmittance of light of a liquid crystal layer is optimized for each of RGB; and Japanese Laid-Open Patent Publication No. 2001-290149 discloses a method in which difference in retardation Re between the liquid crystal cell and the optical compensation films is optimized in each of RGB regions of the RGB filter. These publications, however, provide onlymention of adjusting wavelength-dependence of a liquid crystal cell, and no mention adjusting wavelength-dependence of an optical compensation film.
Japanese Laid-Open Patent Publication Nos. 2004-184864 and 2004-212938 provide mentions of wavelength-dependence characteristics of the optical compensation films. According to both publications, the wavelength-dependence in Re of an optically anisotropic film is defined as α, which is equal to Re(400 nm)/Re(550 nm), a ratio of the Re value measured at 400 nm to the Re value measured at 550 nm. Considering wavelength-dependence characteristics of a rod-like liquid crystal in a cell of an actual liquid crystal panel, it is important to adjust α<1.2 so as to make agreement of the dispersion characteristics between the cell and the optically anisotropic layers, in terms of achieving desirable display quality in the black state. These publications, however, provide no mention of specific means for lowering the wavelength-dependence αof optically anisotropic layers smaller than 1.2. Japanese Laid-Open Patent Publication Nos. H7-281028, H9-104656, H9-117983, 2000-111734 and 2000-111915 disclose techniques of controlling desired characteristics by mixing liquid crystal compounds and non-liquid crystal compounds which compose the optically anisotropic layers. These publications describe means for controlling or improving temperature of alignment, transition temperature, average angle of alignment, twist alignment property, molecular arrangement, and durability of the optically anisotropic layers, but do not disclose how to control the wavelength-dependence characteristics; and the present invention provides the technique.